Did the 74 duster come with 225 or 198 origionally???

cudamark said

My understanding is the 198 was made for mileage. Since adding smog requirements in the early 70's the 170 didn't have power to do the job.

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That's most of it, but there's more. Since the 198 uses the same block as the 225, Mopar could cut costs and simplify manufacturing. To get the piston back towards the top of the block for good compression, the 198 has the longest rods of any /6.